Time division duplex front end module

ABSTRACT

An RF module adapted for direct surface mounting to the top surface of the front end of the motherboard of a wireless base station such as, for example, a femtocell. The module comprises a printed circuit board having a plurality of direct surface mounted electrical components defining respective signal transmit and receive sections for RF signals. The signal transmit section is defined by at least a power amplifier, a coupler, and a lowpass filter. The signal receive section is defined by at least a receive bandpass filter and a low-noise amplifier. A lid covers selected ones of the electrical components except for at least the power amplifier. An RF switch is located between and interconnects the respective transmit and receive sections to an antenna pin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part non-provisional applicationwhich claims the benefit of U.S. application Ser. No. 11/452,800 filedon Jun. 14, 2006; U.S. application Ser. No. 11/823,735 filed on Jun. 28,2007; and U.S. Provisional Application Ser. No. 60/936,201, filed onJun. 19, 2007, the disclosures of which are explicitly incorporatedherein by reference as are all references cited therein.

FIELD OF THE INVENTION

The invention relates to a module and, more particularly, to a timedivision duplex radio frequency (RF) module adapted for use on the frontend of a cellular base station such as, for example, a WiMax wirelessfemtocell communication base station.

BACKGROUND OF THE INVENTION

There are currently four types of cellular/wireless communication basestations or systems in use today for the transmission and reception ofW-CDMA, UMTS, and WiMax based cellular/wireless communication signals,i.e., macrocells, microcells, picocells, and femtocells. Macrocells,which today sit atop cellular/wireless towers, operate at approximately1,000 watts. The coverage of macrocells is in miles. Microcells, whichare smaller in size than macrocells, are adapted to sit atop telephonepoles, for example, and the coverage is in blocks. Microcells operate atapproximately 20 watts. A smaller yet microcell requires about 5 wattsof power to operate. Picocells are base stations approximately 8″×18″ insize, are adapted for deployment inside buildings such as shoppingmalls, office buildings or the like, and output about 0.25 watts ofpower. The coverage of a picocell is about 50 yards. Femtocells outputabout 0.10 watts of power and are used in the home.

All of the picocells and microcells in use today include a “motherboard”upon which various electrical components have been individually mountedby the customer. A front end portion of the motherboard (i.e., the RFtransceiver section thereof located roughly between the picocell antennaand mixers thereof) is currently referred to in the art as the “node Blocal area front end,” i.e., a portion of the femtocell, picocell, ormicrocell on which all the radio frequency control electrical componentssuch as, for example, the filters, amplifiers, couplers, inductors andthe like have been individually mounted and interconnected.

While the configuration and structure of the current motherboards hasproven satisfactory for most applications, certain disadvantagesassociated with the current front end RF configuration thereof includeperformance, the costs associated with a customer's placement ofindividual RF components onto the motherboard during assembly, and thespace which such RF components occupy on such motherboards.

There thus remains the need for increased RF component performance and areduction in both the cost of these motherboards and the space occupiedby the RF components on such motherboards. The present inventionprovides a compact front end RF component module particularly adaptedand structured for the transmission and reception of WiMax signals whichaddresses and solves the above-identified needs.

SUMMARY OF THE INVENTION

The present invention relates generally to a radio frequency (RF) moduleadapted for use on the front end of a wireless base station such as afemtocell, picocell, or microcell base station. The RF module includes aprinted circuit board/substrate having a plurality of electricalcomponents mounted directly thereto and adapted to allow for thetransmission and reception of wireless signals between the antenna ofthe cell on one end and the respective input and output pads on themotherboard of the cell at the other end.

A first section on the printed circuit board/substrate defines atransmit path for RF signals and includes at least the followingelectrical components mounted thereon: a power amplifier, a coupler anda lowpass filter.

The module includes a second section on the printed circuitboard/substrate which defines a receive path for RF signals and includesat least the following electrical components mounted thereon: a receivebandpass filter and a low-noise amplifier.

An RF single pole double throw (SPDT) switch is located between andinterconnects the respective transmit (Tx) and receive (Rx) sections toan antenna pin.

A lid is adapted to cover selected ones of the electrical componentsmounted to the printed circuit board. At least the power amplifier ispreferably located outside the lid. A plurality of through-holes or viaslocated below the amplifier are adapted to define a sink for heatcreated by the power amplifier.

Other advantages and features of the present invention will be morereadily apparent from the following detailed description of thepreferred embodiment of the invention, the accompanying drawings, andthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention can best be understood by thefollowing description of the accompanying FIGURES as follows:

FIG. 1 is a simplified block diagram depicting the flow of wirelesssignals being transmitted and received through the various RF componentsdefining the time division duplex front end module of the presentinvention;

FIG. 2 is an enlarged simplified perspective view of a time divisionduplex front end module in accordance with the present invention;

FIG. 3 is an enlarged simplified plan view of the front or top surfaceof the printed circuit board of the front end module of the presentinvention with the lid removed therefrom; and

FIG. 4 is an enlarged simplified plan view of the back or bottom surfaceof the printed circuit board of the front end module of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While this invention is susceptible to embodiments in many differentforms, this specification and the accompanying FIGURES disclose only onepreferred simplified embodiment as an example of the present inventionwhich is adapted for use in a picocell. The invention is not intended,however, to be limited to the embodiment so described and extends, forexample, to femtocells and microcells as well.

FIG. 1 is a simplified block diagram of the RF (radio frequency) frontend module, generally designated 20, constructed in accordance with thepresent invention and adapted for use in connection with a wireless basestation including, for example, a WiMax femtocell, picocell, ormicrocell.

As described in more detail below, the TDD (time division duplex) WiMaxfront end module 20 utilizes filtering with two filters: a receive Rxbandpass filter 36, and a transmit Tx lowpass filter 28. The module 20also includes a power amplifier (PA) 26, a low-noise amplifier (LNA) 39and other appropriate RF components. In the embodiment shown, all of theappropriate RF components are of the discrete surface-mountable type.

Module 20 is adapted to replace all of the discrete RF components thatwould be typically individually mounted and used in a WiMax Node B localarea front end. Module 20 allows customers to select different valuesfor receiver sensitivity, selectivity, and output power. Moreover,module 20 is RoHS compliant and lead-free. Some of the features of themodule 20 as introduced above and described in more detail below includethe scalable power amplifier 26 capable of delivering about 25 dBm atthe antenna port; the above-identified filters 28 and 36 offeringexcellent isolation and harmonic suppression; and the low noiseamplifier 39.

Table 1 below summarizes the proposed operational parameters andcharacteristics of the time division duplex front end module of thepresent invention:

TABLE 1 Typical Specifications Nominal channel bandwidth: 20 MHzModulation: 64 QAM Antenna switching speed <1 usec TRANSMIT Frequencyrange 2496-2692 MHz PA supply voltage 5 V PA current drain 650 mA Power@ antenna port 25 dBm EVM @ 25 dBm 2.5% Tx gain 23 dB RECEIVE Frequencyrange 2496-2692 MHz LNA supply voltage 3.3 V LNA current drain 15 mANoise figure 2.2 dB IIP3 3 dBm Rx gain 14 dB Attenuation (.1-1796 MHz)−45 dB 2396 MHz −27 dB 2790 MHz −27 dB Temp range: −40° C.-85° C.

Referring now in particular to FIG. 1, it is understood that module 20is defined by a plurality of RF electrical components and pinsassociated with a substrate 22 and defining respective RF signaltransmit and receive sections or paths. Initially, and as shown in FIG.1, the lower RF transmit section or path of module 20 includes a firstTx (transmit) signal input pin 17 adapted to be coupled to acorresponding Tx (transmit) signal pad on the motherboard (not shown) ofa picocell or microcell. Pin 17 in turn is coupled to a Tx PA (transmitpower amplifier) 26 which, in turn, is coupled to a coupler 30 which, inturn, is coupled to a Tx LPF (transmit low pass filter) 28.

VPA (power amplifier supply voltage) is adapted to be supplied to poweramplifier 26 through pin 15. PA bias is adapted to be measured throughpin 1 coupled to power amplifier 26. In accordance with the presentinvention, a portion of the transmit signal is split off from coupler 30and passed to a power detect pin 3. The Tx LPF 28 is, in turn, coupledto an RF SPDT (single pole double throw) switch 29. The switch 29, inturn, is coupled to an antenna via antenna pin 11. Voltage is suppliedto the module 20 through the V supply (voltage supply) pin 9 coupled toswitch 29. The voltage supplied to module 20 is controlled via andthrough V_(CTRL) (voltage control) pin 13, also coupled to the switch29. In another embodiment, the V_(CTRL) pin 13 can be omitted and theswitching function can be facilitated with the use of only one voltageinput pin (i.e., pin 9).

All of the pins associated with the substrate 22, including antenna pin11, extend between the top and bottom surfaces of the module 20 and areadapted to be direct surface mounted into coupling relationship withcorresponding pads (not shown) of a picocell or microcell such as, forexample, the antenna pad thereof to allow for the transmission of thesignals which have passed through the RF signal transmission section ofmodule 20.

Referring to FIGS. 1-4, it is thus understood that the Tx (transmit) RFwireless signal is adapted to travel from thefemtocell/picocell/microcell motherboard into and up through thesubstrate 22 of module 20 via Tx input pin 17 extending between thelower and upper substrate surfaces, and then from Tx input pin 17 intoand through power amplifier 26, coupler 30, lowpass filter 28, switch29, antenna pin 11, and then back down through the substrate 22 viaantenna pin 11 extending between the upper and lower substrate surfacesand into the motherboard antenna pad in direct surface contact withmodule antenna pin 11.

The top receive section or path of the signals being received (i.e., Rxsignals) from the femtocell, picocell, or microcell antenna (not shown)and transmitted through the module 20 will now be described also withreference to FIGS. 1-4 which shows the Rx signal being transmitted andpassed in a left to right, clockwise direction from the picocell ormicrocell antenna (not shown) through the module antenna pin 11 and theninitially through the switch 29.

Switch 29 is, of course, adapted and structured as known in the art toallow the same to switch from the passage of Tx signals out of themodule 20 through the antenna pin 11 to the passage of Rx signals intoand through the module 20 from the antenna pin 11. Thus, and as shown inFIG. 1, the Rx signal is adapted to pass and travel in a generalclockwise direction through the switch 29 and into Rx bandpass filter 36and LNA (low noise amplifier) 39. Voltage is supplied to low noiseamplifier 39 via LNA supply voltage pin 8 coupled thereto.

From the low-noise amplifier 39, the Rx signal then passes through RxO/P (output) signal pin 7 which, in turn, is adapted to extend betweenthe front and back surfaces 23 and 27 of the module 20 for directsurface coupling to the corresponding Rx output signal pad (not shown)on the motherboard of the picocell or microcell.

FIGS. 2-4 depict one simplified embodiment of a module 20 adapted andstructured to be direct surface mounted to the front end of a WiMax TDD(time division duplex) femtocell, picocell, or microcell. It isunderstood, however, that the module embodiment of FIGS. 2-4 differsfrom the module embodiment of FIG. 1 in that, in the FIGS. 2-4embodiment, PA power is detected through the use of a VDET pin 3 insteadof a coupler as in the FIG. 1 embodiment.

By way of background, it is understood that module 20 of the presentinvention as depicted in FIGS. 2-4 measures about 19.0 mm in width, 27.0mm in length, and 6.0 mm max. in height (with the lid secured thereon),and is adapted to be mounted to the motherboard of a WiMax picocellmeasuring about 8 inches by 18 inches which, as described above, isadapted for use as a wireless signal transfer base station inside abuilding such as a shopping mall or office complex.

In accordance with the present invention and referring to FIGS. 2-4,module 20 initially comprises a printed circuit board or substrate 22which, in the embodiment shown, is preferably made of multiple layers ofGETEK® or the like dielectric material and is about 1 mm (i.e., 0.040inches) in thickness. Although not shown in any of the FIGURES, it isunderstood that predetermined regions of both the upper and lowersurfaces 23 and 27 of the substrate 22 are covered with copper or thelike material and solder mask material, both of which have been appliedthereto and/or selectively removed therefrom as is known in the art tocreate the desired copper, dielectric, and solder mask regions andelectrical circuits which interconnect the various electricalcomponents. The metallization system is preferably ENIG, electrolessnickel/immersion gold over copper.

A lid 45 (FIG. 2), which is adapted to cover a portion of the topsurface 23 of the printed circuit board 22, is preferably brass with aCu/Ni/Sn (copper/nickel/tin) plated material for ROHS compliancepurposes. Lid 45 is adapted to act both as a dust cover and a Faradayshield.

As described above, generally rectangularly-shaped substrate 22 has topor front surface 23 (FIGS. 2 and 3), a bottom or back surface 27 (FIG.4), and an outer peripheral circumferential edge defining respectiveupper and lower faces or edges 42 and 44 and side faces or edges 46 and48 (FIGS. 2-5). Although not described in any detail, it is understoodthat, in a preferred embodiment, substrate 22 will be comprised of aplurality of stacked laminate layers of suitable dielectric materialsandwiched between respective layers of conductive material as is knownin the art such as, for example, a bottom RF ground plane layer, an RFintermediate signal layer, a top RF ground layer, and a topmost DC/RFlayer plus ground layer.

Castellations 35 (FIGS. 2-4) are defined and located about the outerperipheral edge of board 22. Castellations 35 define the various groundand DC voltage input/output pins of the module 20. Castellations 35 aredefined by metallized semicircular grooves which have been carved out ofthe respective edges 42, 44, 46 and 48 and extend between the respectivetop and bottom surfaces 23 and 27 of the substrate 22. In the embodimentshown, the castellations 35 are defined by plated through-holes whichhave been cut in half during manufacturing of the substrates from anarray. Castellations 35 extend along the length of the respective edgesof substrate 22 in spaced-apart and parallel relationship. In theembodiment shown, the top substrate edge 42 defines seven spaced-apartcastellations 35, the lower substrate edge 44 defines five spaced-apartcastellations 35, the side substrate edge 46 defines three castellations35, and the opposed side substrate edge 48 defines one castellation 35.

The outer surface of each of the respective castellations 35 is coatedas by electroplating or the like, with a layer of copper or the likeconductive material which is initially applied to all of the surfaces ofthe substrate 22 during the manufacturing of the substrate 22 as isknown in the art and then removed from selected portions of the surfacesto define the copper coated castellations 35. Castellations 35 and, morespecifically, the copper thereon creates an electrical path between topsurface 23 and bottom or back surface 27 of substrate 22.

Although not shown, it is understood that the copper extends around boththe top and bottom edges of each of the castellations 35 to define padsof copper or the like conductive material on the top surface 23 ofsubstrate 22 and surrounding the top or front edge of each of therespective castellations 35; and a plurality of pads extending inwardlyfrom the bottom or back edge of each of the castellations 35 on thebottom surface 27 of substrate 22 which allow the module 20 to bedirectly surface mounted by reflow soldering or the like, tocorresponding pads located on the surface of the motherboard of thepicocell (not shown).

Although not disclosed in any detail, it is understood that respectiveones of the castellations define respective voltage input/output pinswhile other ones of the castellations 35 define pins adapted for directcoupling to the ground copper layer applied to both of the surfaces 23and 27.

Conductive vias 38 defined in the board 22 define the respective RFcomponent signal input/output and antenna pins 7, 11, and 17 of themodule 20. Vias 38 extend through the substrate 22 between the substratesurfaces 23 and 27 thereof and, as known in the art, define an interiorcylindrical surface which has been plated with copper or the likeconductive material. In accordance with the present invention, the useof vias 38 which are spaced from the respective substrate edges insteadof castellations 35 defined in respective substrate edges insures aconstant 50-ohm characteristic impedance.

Pinouts 1 and 3 extend along the bottom longitudinal edge 44 of board22. Pinout 7 extends along the side longitudinal edge 48. Pinouts 8, 9,and 13 extend along the top longitudinal edge 42 of board 22. Pinout 17extends along the side longitudinal edge 46 of board 22.

With reference to FIGS. 2 and 3, power amplifier 26 (together with theother components which are part of the Tx signal path) is preferablylocated in an area of the printed circuit board 22 not intended to becovered by the lid 45, to allow for the dissipation of heat created bythe amplifier 26 and also to reduce the transfer of heat created by theamplifier 26 to any of the electrical components located under the lid45.

More specifically, it is understood that, in the preferred embodiment,power amplifier 26 is generally centrally located on the left hand halfof the top or front surface 23 of the substrate/board 22. Pinout 13extends generally opposite the top edge of power amplifier 26 alonglongitudinal board edge 42. Pinouts 1 and 3 extend generally along thebottom edge of power amplifier 26 along the length of bottomlongitudinal board edge 44. Pinout 17 extends generally opposite theleft side edge of power amplifier 26 along (but spaced inwardly from)board side edge 46.

In the embodiment shown, a first set of appropriate resistors andcapacitors 101, 102, 103, 104, 105, 106, and 107 are all generallylocated and fixed on the top or front surface 23 of board 22 generallybelow the power amplifier 26 and, more specifically, between the poweramplifier 26 and the lower longitudinal edge 44 of board 22.

A second set of appropriate resistors, capacitors, and inductors 108,109, 110, 111, 112, and 113 are all generally located and fixed on thetop or front surface 23 of the board 22 to the left of the poweramplifier 26 and, more specifically, between the power amplifier 26 andthe left side longitudinal edge 46 of the board 22.

A third set of appropriate resistors and capacitors 114, 115, 116, and117 are all generally located and fixed on the top or front surface 23of the board 22 generally above the top edge of power amplifier 26 and,more specifically, between the power amplifier 26 and the toplongitudinal edge 42 of board 22.

Tx low pass filter 28 is located and fixed on the left half of the topor front surface 23 of the board 22 generally between the right sideedge of the power amplifier 26 and the left edge of the lid 45.

A fourth set of appropriate resistors, capacitors and inductors 118,119, 120, and 121 are all located and fixed on the top surface 23 of theboard 22 generally between the power amplifier 26 and the Tx low passfilter 28.

Capacitors 122 and 123 are located the top surface 23 of the board 22generally above Tx low pass filter 28 and, more specifically, betweenthe Tx low pass filter 28 and the top longitudinal edge 42 of board 22.

RF switch 29, Rx bandpass filter 36, and Rx low noise amplifier 39 areall generally located on the right half of the board 22 and adapted tobe located below the lid 45. More specifically, Rx bandpass filter 36 isseated on and covers a substantial portion of the lower portion of theright half of the top or front surface 23 of the board 22. RF switch 29and Rx low noise amplifier 39 are both generally located above the Rxbandpass filter 36 and, more specifically, between the top longitudinaledge of the Rx bandpass filter 36 and the top longitudinal edge 42 ofthe board 22.

Pinout 7 extending along (but spaced inwardly from) the board side edge48 is located generally opposite the right side edge of the Rx low noiseamplifier 39. Pinout 11 extending along (but spaced inwardly from) theboard top longitudinal edge 42 is located generally opposite the topedge of the RF switch 29.

Appropriate capacitors 124, 125, and 126 surround RF switch 29.Appropriate capacitors, resistors, and inductors 127, 128, 129, 130,131, 132, 133, and 134 surround Rx low noise amplifier 39.

Referring to FIGS. 2 and 3, lid 45 includes a top wall or roof 46, afirst pair of respective opposed side walls 49 a and 49 b, and a secondpair of respective opposed side walls 51 a and 51 b, all adapted todepend and extend generally perpendicularly downwardly from theperipheral edges of the roof 46 to define the lid when the walls arefolded during assembly. Each of the walls 49 a, 49 b, 51 a and 51 b inturn defines a lower longitudinal terminal edge 53. The edge 53 of eachof the side walls 49 a and 49 b in turn defines at least twospaced-apart tabs 50 a and 50 b projecting downwardly therefrom andadapted to be fitted into respective through-slots or castellations 37defined in the top surface 23 of the board 22 for locating and securingthe lid 45 to the board 22 in a grounded relationship with the board 22wherein the edges 53 of the respective lid walls 49 a, 49 b, 51 a and 51b are seated over respective elongate ground strips (not shown) definedon the board top surface 23, thus providing and defining a grounded lid45.

As also shown in FIG. 4, a plurality of through-holes or vias 136 aredefined and formed on the board 22 beneath the region where the poweramplifier 26 is seated on the board 22 to define a heat sink for theheat created by power amplifier 26. Through-holes 136 could bedouble-plated with copper or the like material for added thermalconductivity and likewise extend through the board 22.

The process for assembling a module 20 involves the following steps.After the substrate/board 22 has been fabricated, i.e., once all of theappropriate and desired copper castellations, copper strips, coppervias, copper pads, and copper through-holes have been formed thereon asknown in the art, Ag/Sn (silver/tin) solder is screen printed onto a2.6″ by 4.6″ printed circuit board array and, more particularly, ontothe surface of each of the appropriate solder pads and strips defined onthe array following the application of predetermined layers and stripsof solder mask material as known in the art. Solder is applied to thesurface of all of the designated copper strips, pads and regions and allof the desired and appropriate electrical components including all ofthe filters defining the module 20 are then appropriately placed andlocated on the array.

Although not described in any detail, it is understood that theparticular selection, number, placement, and values of the appropriateresistors, capacitors, and inductors may vary depending upon the desiredend application and performance characteristics of the module 20.

The lid 45 is then placed over the appropriate portion of the board 22as described above into a soldered coupled relationship wherein the tabs50 a and 50 b thereof are fitted into appropriate castellations/slots 37defined in the board 22 thereby appropriately locating and securing thelid 45 to the board 22.

To complete the manufacturing process, the module 20 is then reflowsoldered at a maximum temperature of 260° C. so as to couple all of thecomponents and lid 45 to the board. Finally, the array is diced up as isknown in the art and the individual modules 20 are then final tested andsubsequently “taped and reeled” and readied for shipment.

While the invention has been taught with specific reference to anembodiment of the module adapted for use on the front end of a picocell,it is understood that someone skilled in the art will recognize thatchanges can be made in form and detail such as, for example, to theselection, number, placement, interconnection values, and patterns ofthe various RF elements and circuits, without departing from the spiritand the scope of the invention as defined in the appended claims. Thedescribed embodiment is to be considered in all respects only asillustrative of one embodiment and not restrictive.

1. An RF module adapted for direct-surface mounting to the front end ofthe motherboard of a cell, the module comprising: a substrate includingtop and bottom surfaces; a first section on said substrate defining atransmit path for RF signals and including at least the followingelectrical components: a power amplifier, a coupler, and a lowpassfilter; a second section on said substrate defining a receive path forRF signals and including at least the following electrical components: areceive bandpass filter and a low-noise amplifier; and an RF switchbetween and interconnecting said respective first and second sections toan antenna pin.
 2. The RF module of claim 1 further comprising a lidadapted to cover at least said receive bandpass filter and saidlow-noise amplifier.
 3. An RF module adapted for direct surface mountingto a front end of a motherboard of a wireless base station and adaptedto transmit and receive RF signals, the module comprising: a signaltransmit section on a circuit board including at least a poweramplifier, a coupler, and a lowpass filter; and a signal receive sectionon said circuit board including at least a receive bandpass filter and alow-noise amplifier.
 4. The RF module of claim 3 further comprising alid adapted to cover selected ones of the electrical components mountedon said printed circuit board.
 5. The RF module of claim 4, wherein atleast said receive bandpass filter and said low-noise amplifier arelocated under said lid.
 6. The RF module of claim 4, wherein said poweramplifier is located outside said lid and said printed circuit boarddefines a plurality of through-holes located below said power amplifier.7. The RF module of claim 3, wherein a switch is located between saidrespective signal transmit and receive sections.
 8. An RF module adaptedfor direct surface mounting to a front end of a motherboard of awireless base station, said module including a printed circuit boardhaving a plurality of electrical components mounted thereon and adaptedto allow for the transmission and reception of wireless signals betweenthe antenna of said wireless base station on one end and the respectiveinput and output pads on said motherboard of said wireless base stationat the other end.
 9. The RF module of claim 8 comprising at least areceive bandpass filter and a transmit lowpass filter all direct surfacemounted to said printed circuit board of said module.
 10. The RF moduleof claim 9 further comprising a power amplifier and a low-noiseamplifier, both also direct surface mounted to said printed circuitboard of said module.
 11. The RF module of claim 10 wherein said poweramplifier, a coupler, a lowpass filter and a switch define a transmitpath for RF signals.
 12. The RF module of claim 11 wherein said switch,said receive bandpass filter, and said low-noise amplifier define areceive path for RF signals.
 13. The RF module of claim 12 furthercomprising a lid adapted to cover at least said low-noise amplifier andsaid receive bandpass filter.